A microspeaker is provided in a portable device, etc, to generate the sound. With recent developments of mobile devices, the microspeaker has been mounted in various mobile devices. In particular, the latest mobile devices tend to have a light weight, small size, and slim shape to facilitate portability, and accordingly, the microspeaker mounted in the mobile devices is required to have a small size and slim shape.
However, for a microspeaker having a small size and slim shape, an area of a diaphragm decreases, and a size of a resonance space, in which the sound generated by the vibration of the diaphragm is resonated and amplified, also decreases, as a result of which a sound pressure decreases. Such decrease in the sound pressure is particularly pronounced at low frequencies.
FIG. 1 illustrates one example of a conventional microspeaker enclosure. For the conventional microspeaker enclosure, a microspeaker A is mounted in a space defined in the enclosure by an upper casing 11 and a lower casing 12, and the remaining space, which is left after the mounting of the microspeaker A, is used as a resonance space (back volume). Here, a sound absorber 20 is arranged in the resonance space to restrict reflected waves of the sound generated by the microspeaker A, thereby preventing the distortion of the sound caused by standing waves.
FIG. 2 illustrates another example of the conventional microspeaker enclosure. In the conventional microspeaker enclosure of FIG. 2, a microspeaker A is mounted in a space defined in the enclosure by an upper casing 11 and a lower casing 12, and the remaining space, which is left after the mounting of the microspeaker A, is used as a resonance space (back volume). In the conventional microspeaker enclosure of FIG. 2, in order to overcome the reduction of the sound pressure, which results from the small size and slim shape, porous materials 30 are arranged in the resonance space to enhance a low-frequency sound pressure, such that the porous materials 30 adsorb air molecules to define a virtual acoustic space, which increases low-frequency SPL and decreases low-frequency THD.
A pouch, etc. may be used to fill the porous materials 30 in the resonance space in such a manner that the porous materials 30 are filled in a pouch formed from a screen filter material, and then the pouch filled with the porous materials 30 is attached to the resonance space.